1. Technical Field
The present invention relates to a rotor in which the structure of permanent magnets embedded in a rotor core is improved, and a permanent magnet-embedded motor.
2. Description of Related Arts
A permanent magnet-embedded motor (interior permanent magnet (IPM) motor) has a structure in which a plurality of permanent magnets is evenly embedded inside a rotor core in a circumferential direction. However, the IPM motor has a problem in that apart of magnetic flux of the permanent magnet short-circuits the inside of the rotor core, thereby reducing torque.
As a technology of improving the torque of the IPM motor, an IPM motor is disclosed in which the torque is improved by setting a ratio of an outer radius R0 of the rotor and an innermost radius R1 of the permanent magnet to R1/R0>0.85 (see Japanese Patent No. 3592948, for example).
Also, another IPM motor is disclosed in which the torque is improved by using two or more permanent magnets for one magnetic pole (see Japanese Patent No. 3835231, for example).
Incidentally, according to the technology of Japanese Patent No. 3592948, a rotor core form includes a rib portion which connects an outer peripheral portion and an inner peripheral portion of the rotor core, in which the width of the rectangular permanent magnet has a limit value determined by combination of the ratio R1/R0 and the thickness of the rib portion. Due to the limit value, the amount of magnetic flux of the permanent magnet is limited. Further, there are numerous short-circuit fluxes in the permanent magnet via the rib portion, thereby reducing the torque.
Also, according to the technology in Japanese Patent No. 3835231, numerous permanent magnets are used and the cost is increased not only for the permanent magnets but also for manufacturing.
The present invention has been made in view of the foregoing circumstances, and an object of the present invention is to provide a permanent magnet-embedded motor and a rotor thereof, capable of reducing the short-circuit flux of the permanent magnet and improving the torque without increasing the manufacturing cost.